The Real Adam Always course correcting

Changing git submodule URLs

Pro-tip: if you’re using submodules with Git to manage dependencies (say Rails plugins), you can get yourself into trouble. Like half-a-day of wasted trouble.

The rub comes when you need to make a change to some plugin. Suppose you were using Brain Buster for your captcha and then decided you need to make a change. The git submodule command doesn’t really seem to offer a way to change the URL for the submodule. Let me summarize what I’ve found in trying to do this.

The Wrong Way

• Fork/create your own version of the submodule in question
• Change the URL for the submodule in .git/config and .gitmodules
• Cross your fingers and hope for the best

The Right Way

• Fork/create your own version of the submodule in question
• Remove references to the existing submodule in .git/config, .gitmodules and nuke the submodule directory
• Commit
• Add the new submodule URL
• Commit
• Make changes in your submodule
• Commit changes in the submodule (not the parent project)
• Commit the changes in the parent project (otherwise you’ll only get the old version of the submodule in future pulls)
• Enjoy the hair you didn’t have to rip from your scalp

Learn from my mistakes, people.

Adam,

Thanks, I have learned from your mistakes. This yak still has all it’s hair.

Yes, thank you! We’ve been trying to make submodules work for a repository of code shared between several applications, and the things submodules don’t do that svn:externals did (like auto-updating) have been driving us nuts. We’re starting to wonder if it’s more trouble than it’s worth.

Out of interest, what’s Wrong with The Wrong Way? As long as you fix up the repository URL in your local clone of the submodule (e.g. edit its .git/config, or just blow it away and git submodule update from scratch) it seems like it should chug along fine without having to completely nuke and re-add the whole submodule. What gives?